Double deflection system for an electron beam device

Claim 2

In an electron beam device having means for generating a beam of electrons, a magnetic lens for focusing the beam to a point in any image plane, and scanning means for scanning the focused point in the image plane, the coordinates of the center of the scanned point in the image plane being (x 1 y 1 ), the beam normally being incident in the aperture plane of the lens at a location whose coordinates of the center of the beam are (x a , y a ) and at a slope determined by the scanning means, the improvement in the instrument for simultaneously correcting isotropic coma and anisotropic coma aberrations, comprising:

Claim 3

deflection means positioned along the path of the beam prior to entry of the beam into the lens for displacing the intersection of the beam with the aperture plane so that the slope of intersection remains unchanged and so that the coordinates of the center of the beam at intersection (x o and y o ) satisfy the relations x.sub.a = x.sub.o + αx.sub.1 + βy.sub.1 y.sub.a = y.sub.o + αy.sub.1 -βx.sub.1 where α = S 6 /S 8 and β = S 7 /S 8 wherein S 6 , S 7 , and S 8 , are abberration coefficients.

Claim 4

deflection means positioned along the path of the beam prior to entry of the beam into the lens for displacing the intersection of the beam with the aperture plane so that the slope of intersection remains unchanged and so that the coordinates of the center of the beam at intersection (x o and y o ) satisfy the relations x.sub.a = x.sub.o + αx.sub.1 + βy.sub.1 y.sub.a = y.sub.o + αy.sub.1 -βx.sub.1 where α = S 6 /S 8 and β = S 7 /S 8 wherein S 6 , S 7 , and S 8 , are abberration coefficients.

Claim 5

The device of claim 1 wherein said scanning means includes a double deflection system having first and second deflection elements through which the beam passes, each element being capable of deflecting said beam.

Claim 6

The device of claim 2 wherein each element includes means for deflecting the beam in the x direction and means for deflecting the beam in the y direction, the amount of deflection in the x direction being controlled by a control voltage V x and a correction voltage and in the y direction being controlled by a control voltage V y and another correction voltage, said correction voltages being related to α and β.

Claim 7

The device of claim 3 wherein each deflection element is comprised of two pairs of series coupled opposing coils, with a first pair of said coils of said first element deflecting the beam in the x direction and a second pair of said first element deflecting the beam in the y direction, with a third pair of said coils of said second element deflecting the beam in the -x direction and a fourth pair of said second element deflecting the beam in the -y direction, said second element being between said first element and the lens along the beam path.

Claim 8

The device of claim 4 further including a first inverter developing an output equal to -V x , a second inverter developing an output equal to -V y , first and second potentiometers, a first terminal of said first potentiometer having applied thereto V y and the second terminal thereof having applied thereto -V y , a first terminal of said second potentiometer having applied thereto -V x and the second terminal thereof having applied thereto -V x , the taps of said first and second potentiometers being interconnected so that movement of said tap of said first potentiometer toward said first terminal thereof causes movement of said tap of said second potentiometer toward said first terminal thereof, the output of the tap of said first and second potentiometers being V.sub.βy and V - βx respectively, V.sub.βy and V - βx being utilized by the scanning system to form a portion of said correction voltages.

Claim 9

The device of claim 5 further including third and fourth potentiometers, a first terminal of said third potentiometer having applied thereto V x and the second terminal thereof having applied thereto -V x , a first terminal of said fourth potentiometer having applied thereto V y and the second terminal thereof having applied thereto -V y , the taps of said third and fourth potentiometers being interconnected so that movement of said tap of said third potentiometer toward said first terminal thereof causes movement of said tap of said fourth potentiometer toward said first terminal thereof, the output of the taps of said third and fourth potentiometers being V.sub.αx and V.sub.αy, respectively being utilized by the scanning system to form a portion of said correction voltages.

Claim 10

The device of claim 6 wherein said scanning means further includes a first driver coupled to said first and third potentiometers and to said first coil pair for applying a current to said first coil pair proportional to (A 1 V x + A 2 V.sub.αx + A 3 V.sub.βy), a second driver coupled to said second and fourth potentiometers and to said second coil pair for applying a current to said second coil pair proportional to (B 1 V y + B 2 V.sub.αy + B 3 V - βx), a third driver coupled to said first and third potentiometers and to said third coil pair for applying a current to said third coil pair proportional to (C 1 V x + C 2 V.sub.αx + C 3 V.sub.βy), and a fourth driver coupled to said second and fourth potentiometers and to said fourth coil pair for applying a current to said fourth coil pair proportional to (D 1 V y + D 2 V.sub.αy + D 3 V - βx) where the coefficients A 1-4 , B 1-4 , C 1-4 and D 1-4 are selected so that the intersection of the beam with the aperture plane is at (x o , y o ).